theorem Th19:
   for n be Ordinal,L
   for p being Series of n,L holds 1.L*p = p
   proof
     let n be Ordinal, L;
     let p be Series of n,L;
     for i being Element of Bags n holds ((1.L)*p).i = p.i
     proof
       let i be Element of Bags n;
       thus ((1.L)*p).i = (1.L)*p.i by POLYNOM7:def 9 .= p.i;
     end;
     hence thesis;
   end;
